This invention relates to hydraulically powered apparatus for digging and transplanting trees and the like, and more particularly to a vehicle-mounted apparatus in which reciprocating blade assemblies mounted to a horizontally disposed frame include an improved arrangement of means for guiding and firmly supporting the spade blades as they penetrate the soil.
There are many transplanting devices commercially available to nurserymen, of the kind in which an assembly of reciprocating blades is adapted to converge into the ground surrounding the plant so as to form a "rootball", a well-formed excavated portion of the roots together with the earth in which they are imbedded. The plant, transported with its rootball intact, may continue to receive nourishment until it is replanted. If the plant is to be moved to a distant location, the rootball may first be freed from the transporting device and placed into a burlap-lined wire basket.
It has been recognized that the very substantial bending stresses to which the blades of a transplanting device of this kind are subject can result in failure of the blades to converge properly and provide an intact rootball about the plant. Flexing of the blades and stresses on their associated support can also lead to wear, jamming or break-down of the mechanism.
Various expedients have been adopted in transplanters known to the prior art which are intended to compensate for the stresses encountered by digger blades. For example, the prior device disclosed in Grover U.S. Pat. No. 3,713,234 employs a tubular tower (guide tube) and a thrust tube telescopically enveloping the tower for directing the blade along the desired path. However, the arrangement of bolting the blade to the outside of the thrust tube cannot afford satisfactory bracing against the radially outwardly directed forces tending to spread the digger blades. Moreover, the shaping of the blades themselves in the Grover device includes a flat central portion inherently susceptible to the radially outward flexing forces and not adapted to form a rounded rootball for placement into conventional baskets, which typically are 15 inch diameter and circular at the bottom.
Other prior art devices employ more complex guiding and alignment mechanisms operatively connecting the reciprocating blade to the tower along which its path is determined, for example LeMond U.S. Pat. No. 4,286,398 (rollers mounted in housing) and Stocker U.S. Pat. No. 4,341,025 (rack-and-pinion). These are also subject to failure and misalignment arising from these "spreading" force on blades convergingly penetrating the earth and, additionally, tend to jam or to require frequent removal of dirt and debris entering the blade guiding mechanisms in use.
The problem of binding and jamming because of obstruction of mechanisms by debris has been the particular focus of other prior art devices, for example Weeks U.S. Pat. No. 5,081,941 which discloses an assembly of arcuate converging towers along each of which a slide assembly moves, a blade being affixed to the outside of the slide assembly. The slide assembly includes a housing adapted to slide along the tower on an arrangement of plastic weir pads and brass weir pads intended to provide lower friction, deformable sliding surfaces. Again, however, the blades are affixed only to corresponding outer surfaces of the sliding members, so that much of the bending stress encountered in use is borne by the blades themselves and by hydraulic cylinder linkages to the slide assembly.
It is also typical of the aforementioned and other like devices in the prior art that the portion of the blade which is positively supported against lateral movement and flexion is considerably shorter than the "free" lower portion which enters the ground. Typically, a 4 ft. long spade is supported at its upper end by only about 1 ft. of "anchor". In the result, a relatively small angular deflection at the tip of a blade in use translates to a considerable flexing force over the short supported portion, leading to misalignment and jamming of the mechanism.